In recent years, 2,3,3,3-tetrafluoropropene (HFO-1234yf) has attracted attention as a new refrigerant to replace 1,1,1,2-tetrafluoroethane (HFC-134a) which is a greenhouse gas. In this specification, with respect to a halogenated hydrocarbon, after its chemical name, an abbreviated name of the compound is shown in brackets, and in this specification, as the case requires, instead of the chemical name, its abbreviated name is used.
As a process for producing HFO-1234yf, for example, a process is known wherein 1,1-dichloro-2,2,3,3,3-pentafluoropropane (HCFC-225ca) is subjected to dehydrofluorination with an aqueous alkaline solution in the presence of a phase-transfer catalyst to obtain 1,1-dichloro-2,3,3,3-tetrafluoropropene (CFO-1214ya), which is then used as synthetic raw material and reduced by hydrogen to obtain HFO-1234yf.
However, this process has problems such that it requires multistage reactions whereby installation costs tend to be high, and distillation/purification of the intermediate product and the final product is difficult.
Patent Document 1 discloses that different types of hydrochlorocarbon compounds (e.g. chloromethane and chlorodifluoromethane) are combined and heated at 845±5° C. in the presence of steam for dehydrochlorination and condensation, whereby fluorine atom-containing olefins such as HFO-1234yf and 1,1-difluoroethylene (VdF) are formed.
Further, Patent Document 2 discloses a method for obtaining HFO-1234yf by heating and decomposing a mixture of chloromethane and chlorodifluoromethane or tetrafluoroethylene at a temperature of from 700 to 950° C. by a common heating means such as an electric heater in a reactor.
However, in the method disclosed in Patent Document 2, as the retention time increases, formation of high boiling products as by-products and carbonization of raw material are likely to occur whereby the reactor is likely to get blocked, and by the influence of an acid component formed as a byproduct, a special corrosion resistant apparatus (such as a reaction tube lined with platinum) is required, and thus, in consideration of the industrial production, such a method is totally unrealistic.
In the method disclosed in Patent Document 1, the raw material component was not sufficiently subjected to the reaction. For example, the conversion of chloromethane was 17%, and thus, an efficient reaction was not attained. Further, the proportion of VdF in the obtained product was high, whereby it was difficult to say that HFO-1234yf was efficiently produced.